题目
题型:不详难度:来源:
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093428-68894.png)
解析
∴可设圆心C(a,0),其半径为3-a
∴圆C之方程为(x-a)2+y2=(3-a)2
联立抛物线与圆C之方程得:x2-2(a-1)x+6a-9=0
由题意知Δ=4(a-1)2-4(6a-9)=0
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093428-66094.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093429-12772.png)
∴圆C的半径能取到的最大值为
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093428-68894.png)
核心考点
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093422-20126.jpg)
(1)求点M到抛物线C1的准线的距离;
(2)已知点P是抛物线C1上一点(异于原点),过点P作圆C2的两条切线,交抛物线C1于A,B两点,若过M,P两点的直线l垂直于AB,求直线l的方程
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093414-69494.png)
A.![]() | B.![]() |
C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-32034.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-96160.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-73945.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-23876.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-18665.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-16251.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-20556.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-77102.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-64249.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-94567.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-99863.png)
(1)求抛物线
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-73945.png)
(2)过点
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-64249.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-32034.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-63247.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093403-73945.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-13868.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-82858.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093404-83091.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093405-49916.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093351-77995.png)
A.![]() | B.![]() | C.(0,1) | D.(1,0) |
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093344-97710.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093345-15816.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093344-97710.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093345-48253.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093345-50572.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191024/20191024093344-97710.png)
A.![]() | B.![]() | C.![]() | D.![]() |
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